基于序列图像的鲁棒三维重建方法

提出了基于序列图像的鲁棒三维重建方法。首先利用两幅图像的最优参数估计,然后添加新图像并采用稀疏调整,减少图像坐标测量值的最小几何误差。通过对三维结构和摄像机参数进行全局优化处理,以提高重建的鲁棒性。实验结果表明,该方法提高了重建的精度和鲁棒性,并真实地再现了物体的三维模型。     

空间跳跃加速的GPU光线投射算法

光线投射算法是一种应用广泛的体绘制基本算法,能产生高质量的图像,但是时间复杂度较高。实现了一种基于图形处理器的单步光线投射算法,并在此基础上提出了一种基于空间跳跃技术的光线投射算法,以实现加速。采用八叉树组织体数据,利用空间跳跃有效地剔除体数据中对重建图像无贡献的部分,降低了硬件的负载。一个片段程序即可完成光线方向的生成、光线投射、空体素跳跃和光线终止等。实验结果表明,该算法对于内部包含大量空体素的体数据重建能起到明显的加速作用。     

一种基于图像的非均匀单散射参与介质建模方法

针对非均匀单散射参与介质建模问题,提出一种能够保持密度场空间变化细节的建模方法.使用体数据、吸收和散射系数之比分别描述参与介质空间变化的密度分布及光线在其内部的传输特性,通过构建采集图像像素值与它们之间的表达式,将建模问题转化为非线性数值优化问题,求最优解.为了解决高分辨率体数据下大量体素密度值同时求解带来的时间开销大及数值不稳定问题,提出一种符合采集图像像素值明暗分布规律的密度场体数据初始化算法和一种多分辨率体数据逐步求精优化算法;为了快速计算大量体素密度值梯度,提出一种基于GPU的多体素并行梯度计算算法.实验结果表明,提出的方法能够根据采集图像重构烟模型,并保持其细节信息.     

基于MITK的血管三维重建

利用二维血管内超声图像序列重建三维血管模型,并对三维模型进行虚拟剖切,可以方便地看到内部组织,便于观察和诊断.针对血管内超声图像亮度变化小、形状特征不明显和图像分割效果不好等问题,基于MITK平台,采用光线投射算法对二维超声图像序列进行体绘制三维重建.对重建模型进行旋转、缩放和任意平面裁剪等交互操作,裁剪掉一部分无关体素,有助于医生观察血管的内部结构和细节信息.此外,通过调节体素的阻光度值,可以得到层次清晰的三维血管模型.     

GPU并行计算加速的实时可视外壳三维重建及其虚实交互

针对现有的基于图像的三维重建方法难以实现真实物体的快速三维重建,无法满足虚实交互等应用需求的问题,提出一种基于GPU并行计算的实时三维重建及其虚实交互方法.首先把物体所在空间剖分成具有数据独立性的体素集合,结合可视外壳重建算法和精确行进立方体算法并行遍历每个体素得到体素状态序列;然后并行压缩体素状态序列得到非空体素集合,对非空体素进行并行三角形网格化,并利用图形硬件的多重纹理映射和可编程功能进行基于像素的纹理映射;最后假定虚拟物体的粒子为运动受限的拉格朗日流体粒子,重建物体网格顶点为流体边界,通过流体动力学方程的并行光滑粒子动力学方法求解来计算虚实交互.实验结果表明,该方法在GPU上进行完全并行求解,在32×32×32的空间剖分精度下,实现了实时三维重建和20帧/s左右的虚实交互计算,适用于计算机图形学和虚拟现实等领域中的虚实交互应用.     

基于微观图像的加工表面3维形貌重建算法研究

切削加工表面由于微观不平度及镜面效应的存在,使得照射其上的光线具有多次散射及后向散射的特性,从而影响了以工件表面图像3维重建形貌的精度。提出了一种基于二向反射分布函数的表面重建算法,构造了以Hapke模型表达的金属切削表面重建方程。该算法以重建方程离散化为手段,计算出光源和物体的倾角和偏角,得到光源和物体的梯度值,最后采用全微分方程对物体表面高度进行恢复。通过对实际切削加工表面图像3维形貌重建结果与触针式测量结果的对比表明,重建形貌粗糙度轮廓贴近实测粗糙度轮廓,证明了本文算法的准确、有效性,为加工表面3维形貌的重建提供了新的思路和方法。     

基于双视角的可见外壳三维重建研究

针对双目视觉重建方法在三维重建过程中步骤繁琐与重建效果不理想的问题,文中提出了一种基于双视角下可见外壳的三维重建方法。该方法主要借助平面镜成像原理,在不同视角拍摄包含物体与其成像的两幅图像,并根据成像原理确定物体之间的位置关系。通过相机与周围物体的运动关系求得相机参数,实现相机自标定。然后根据阈值分割及区域生长算法处理边缘信息得到目标轮廓,通过可见外壳方法计算侧影轮廓线,连接轮廓线形成重建模型。该方法通过自适应可见外壳种子体素生长在不了解物体先验知识的情况下完成重建。文中对比文献"基于图像轮廓的三维重建方法"中的单视角重建物体方法,提出了双视角重建物体模型方法。实验结果表明,双视角重建方法简单实用,生成的三维模型准确真实。     

多层次感知的多视图三维模型重建

针对基于体素表征的多视图三维模型重建过程中,存在二维视图所包含的空间信息离散,空间网格中体素分布稀疏的问题,提出基于多层次感知的多视图三维模型重建方法,旨在通过对视图级、体素级与物体级信息的多层次感知,重建具有完整结构与局部细节的三维模型。在视图特征提取阶段设计了上下文感知的通道注意力模块来最大限度获取二维视图中潜在空间信息;在三维模型生成阶段,通过体素感知的VoxFocal Loss来促进空间网格中体素生成;在三维模型细化阶段,通过具有物体感知能力的三维判别器来自适应地消除三维模型中冗余体素,生成更具真实感的三维模型。在大型合成数据集ShapeNet和真实世界数据集Pix3D上验证了该方法的有效性与先进性。     

基于PTM模型文物纹理映射算法

针对三维重建物体纹理不真实与不精确问题，提出了基于PTM（Polynomial Texture Maps）模型的文物纹理映射算法，该算法利用了多项式颜色依赖性的特质，采取表征颜色与亮度依赖关系的双二次多项式系数进行存储纹素数据，从而实现在变化的光照条件下重建物体的表面纹理。此外针对原PTM模型中存在的原始采集图像漫反射异常、亮度信息分布不均匀、重建拟合系数不精确，导致的重建图像纹理模糊、存在重影、物体细节纹理缺失等问题，提出了改进多项式的基函数和优化拟合系数的PTM算法以及PTM图像采集设备的优化方法，最后经实验验证，提出的算法使得重建物体纹理的真实性与精确度均得到了有效提高。     

基于非线性最小二乘的图像自适应SR重建以及运动估计

图像超分辨率（SR）重建是利用数字信号处理技术由一系列低分辨率观测图像得到高分辨率图像。为了扩展SR技术的应用范围,提出了一种同时进行图像超分辨率重建和全局运动估计的方法。该方法首先基于最大后验概率(MAP)给出了图像SR重建和运动估计框架,该框架不仅考虑了前后两次迭代所得的HR图像差值对最终重建图像的影响,而且引入了不同LR图像对重建图像的重要性权值,使得算法具有自适应性;然后将总体框架转换为图像SR重建模型和运动估计模型;最后基于非线性最小二乘法对模型进行优化求解,得出了SR重建图像及其全局运动域。实验表明,该方法不仅图像重建效果良好,并有着良好的收敛性。     

Circular camera array system for 3‐D displays based on the reconstruction of parallax rays

Abstract— A circular camera system employing an image‐based rendering technique that captures light‐ray data needed for reconstructing three‐dimensional (3‐D) images by using reconstruction of parallax rays from multiple images captured from multiple viewpoints around a real object in order to display a 3‐D image of a real object that can be observed from multiple surrounding viewing points on a 3‐D display is proposed. An interpolation algorithm that is effective in reducing the number of component cameras in the system is also proposed. The interpolation and experimental results which were performed on our previously proposed 3‐D display system based on the reconstruction of parallax rays will be described. When the radius of the proposed circular camera array was 1100 mm, the central angle of the camera array was 40°, and the radius of a real 3‐D object was between 60 and 100 mm, the proposed camera system, consisting of 14 cameras, could obtain sufficient 3‐D light‐ray data to reconstruct 3‐D images on the 3‐D display.     

从二维系列摄影图片提取剪影重构三维实体的光线跟踪算法

给出了利用二维系列摄影图片提取剪影重构三维实体的一种新算法,即围绕一个三维实体从多个角度拍摄照片,然后从照片中提取出实体的边界,通过基于光线跟踪的、对二维影像的合成得到原物体近似表面的三维点坐标,与传统的基于体像素的算法相比,该算法节省存储空间,近似精度与三维分辨率无直接关系,而且速度有所提高,特别当实体体积较大时,效果明显。     

Fast ray-tracing of rectilinear volume data using distancetransforms

The paper discusses and experimentally compares distance based acceleration algorithms for ray tracing of volumetric data with an emphasis on the Chessboard Distance (CD) voxel traversal. The acceleration of this class of algorithms is achieved by skipping empty macro regions, which are defined for each background voxel of the volume. Background voxels are labeled in a preprocessing phase by a value, defining the macro region size, which is equal to the voxel distance to the nearest foreground voxel. The CD algorithm exploits the chessboard distance and defines the ray as a nonuniform sequence of samples positioned at voxel faces. This feature assures that no foreground voxels are missed during the scene traversal. Further, due to parallelepipedal shape of the macro region, it supports accelerated visualization of cubic, regular, and rectilinear grids. The CD algorithm is suitable for all modifications of the ray tracing/ray casting techniques being used in volume visualization and volume graphics. However, when used for rendering based on local surface interpolation, it also enables fast search of intersections between rays and the interpolated surface, further improving speed of the process     

基于体素相似度的医学图像层间插值方法

断层图像层间插值是医学图像三维重建的一个重要环节,但现有插值算法易引起图像边界模糊或效率低下的不足。为此提出一种基于体素相似度的医学图像层间插值算法。该算法根据断层图像的体素相关性和组织本身特征信息计算其体素的相似度,并利用其相似度对插值点进行分类插值。实验结果表明,和已有的算法比较,新算法较好地提高了插值图像的质量,并且计算量大为减少。     

Priority-driven Ray Tracing

A typical ray tracing algorithm traces a ray through each screen-pixel and spawns secondary rays at ray–object intersection points. Unlike traditional ray tracers which follow these rays recursively, we assign a priority value to each newly spawned ray and insert it into a priority queue. The priority assigned to each ray can be based on a variety of criteria, some of which we explore here. The next ray we trace is always the one with the highest priority in the queue. Occasionally, we trigger display updates when a checkpoint or predefined threshold is reached, providing intermediate images for review and evaluation. Classical ray tracers, once given the rendering specifications, are not controllable by the user. The priority-driven ray tracing, on the other hand, provides the user with a mechanism to steer the rendering and deliver intermediate images amid processing. This paper describes the illumination model of the non-recursive priority-driven ray tracer and evaluates its memory and time requirements. We show that although worst-case memory requirements can be overwhelming, in practice, our method is both useful and feasible. © 1997 by John Wiley & Sons, Ltd.     

GPU‐Based Spherical Light Field Rendering with Per‐Fragment Depth Correction

Image‐based rendering techniques are a powerful alternative to traditional polygon‐based computer graphics. This paper presents a novel light field rendering technique which performs per‐pixel depth correction of rays for high‐quality reconstruction. Our technique stores combined RGB and depth values in a parabolic 2D texture for every light field sample acquired at discrete positions on a uniform spherical setup. Image synthesis is implemented on the GPU as a fragment program which extracts the correct image information from adjacent cameras for each fragment by applying per‐pixel depth correction of rays. We show that the presented image‐based rendering technique provides a significant improvement compared to previous approaches. We explain two different rendering implementations which make use of a uniform parametrisation to minimise disparity problems and ensure full six degrees of freedom for virtual view synthesis. While one rendering algorithm implements an iterative refinement approach for rendering light fields with per pixel depth correction, the other approach employs a raycaster, which provides superior rendering quality at moderate frame rates. GPU based per‐fragment depth correction of rays, used in both implementations, helps reducing ghosting artifacts to a non‐noticeable amount and provides a rendering technique that performs without exhaustive pre‐processing for 3D object reconstruction and without real‐time ray‐object intersection calculations at rendering time.     

基于平板探测器的锥束CT投影图像校正

在分析基于平板探测器的锥束CT投影图像缺陷的产生原因和特性的基础上,提出校正的方法,分别对投影图像进行暗场、像元响应不一致的一步校正和光场不均匀校正、像素坏点去除。通过在同一锥束CT系统中相同电压、电流水平情况下,采集不同积分时间下的空气投影图和相同条件下的暗场图,并对其像素值变化进行分析、拟合和对比,得到系统的线性参数矩阵、光场分布图和坏点位置图。对空气投影图像进行校正,并将其作为不完全参照,计算射线吸收系数,用于锥束CT重建。实验结果表明,该方法能有效去除锥束CT投影图像的噪声,抑制物体重建切片的大量环状伪影的产生,提高锥束CT系统重建图像的质量。     

Using 2- and 2 -dimensional seed filling in view lattice to accelerate volumetric rendering

In this paper we propose new methods for calculating the projection of an opaque 3-dimensional 6-connected volumetric object into a two-dimensional view using 2- and 2 -dimensional seed-filling in the view space. When a 3-dimensional volumetric data set is sampled by parallel rays at a resolution exceeding the Nyquist ratio, the 6-connectivity of objects is maintained from volume lattice to view lattice. Given a seed point for each 6-connected object in the volumetric data set, a seed-filling algorithm may access all sample points in view lattice, while simultaneously composing the rendered view. The algorithms presented in this paper minimize the number of voxels that need to be processed. We implemented these methods on a general purpose computer architecture and tested them with several artificial and real-life medical volumetric data sets. It is shown that the algorithms may be used to speed up the parallel ray casting of opaque medical objects. The actual frame rate achieved by the combined method allows interactive (10 frames/sec) rotation of the object on a common single-processor personal computer without specialized hardware.     

CT图像重建滤波反投影析算法的精度研究

CT是常被用于医学和工业领域的计算机断层成像技术,这是一种优质无损诊断技术,即利用投影数据重建物体断层图像。对于精密部件的检测在图像重建无损检测应用中需要有更高的精度要求,CT应用中期待解决的关键问题是怎么样能直接重建出满足工程目标的CT图像。本文就系统地深入地研究了解析式图像重建算法的精度。在重建算法中滤波反投影（FBP）算法是解析法的根本,所以本文以该算法的实现,利用定积分数值计算方法,根据反投影的特点,提出了基于辛普生公式的精确反投影方法。